This invention relates to a differential assembly for an axle, and more specifically, the invention relates to differential assemblies for which multiple gear ratios is desirable. This invention can also be applied to any mechanical device with any type of bevel gears that requires multiple gear ratios that include hypoid gears, spiral bevel gears, straight bevel gears, and their variations.
Drive axles typically incorporate a differential assembly to permit the wheels on opposing ends of the axle assembly to rotate at different speeds. The differential assembly includes a ring gear that is driven by a pinion, which receives rotational drive from the engine through the transmission. The mechanical relationship between the pinion and ring gear provides a gear ratio which provides a mechanical advantage, or increased torque, to the wheels.
Often it is desirable to provide multiple gear ratios for a given axle, especially for automotive applications. It is desirable to maintain as many common components between the different axle assemblies to minimize costs. The differential assembly may include a differential case with a ring gear supported thereon. The ring gear may be fastened to a flange extending from the differential case. Typically, the pinion and ring gear are changed to provide different ring gear ratios for the different axle assemblies. A smaller diameter pinion is used to provide an increased torque amplification. Obviously, when a different sized pinion is used the ring gear or the differential case must also be changed to align and couple the pinion and ring gear.
If a common differential case and flange location is to be used for multiple gear ratios, the thickness of the ring gear must be increased or decreased so that the pinion will couple the ring gear. That is, for a larger diameter pinion a thinner ring gear must be used, and conversely, for a smaller diameter pinion a thicker ring gear must be used. However, using a thicker ring gear simply to maintain engagement with the pinion is undesirable because it adds unnecessary weight and cost to the ring gear. As a result, a differential case has been used with a different flange location for a range of different gear ratios. This also is undesirable because multiple differential cases must be manufactured which adds cost to the axle assembly. Therefore, what is needed is an axle assembly that uses a common differential case and limited ring gear thickness variation for multiple axle gear ratios.
Sometimes a different pinion offset is desirable in a bevel gearset for an optimized gear design to suit a particular application. A real situation is when a spiral bevel gearset (no offset) is best for one vehicle, while a hypoid gearset (with offset) is ideal for another vehicle. Changing pinion offset typically requires changing major structures such as carrier housing, which is economically inconvenient.
The present invention provides a drive axle assembly including an axle housing having a cavity. A differential case is disposed within the cavity. The ring gear is supported on the differential case such as by fastening the ring gear to a flange extending from the differential case. A pinion cage eccentrically supports the driveshaft and pinion, which are rotatable about a first axis. The pinion cage may be used for different axle assemblies having different gear ratios and pinion offsets. Moreover, the same differential case may be used for the different axle assemblies. The pinion cage is rotatable relative to the carrier housing between first and second positions in which the first axis is spaced from the ring gear first and second distances, respectively. In this manner, the pinion offset and gear mounting distance may be varied. The pinion cage is secured to the housing, preferably by fasteners, in one of the positions to accommodate a particular gearset.
Accordingly, the present invention provides an axle assembly that uses a common differential case and limited ring gear thickness variation for multiple axle gear ratios and pinion offset.